1. Field of the Invention
The present invention relates to a photodetector for performing photodetection with high sensitivity by using an amorphous selenium photoconductor, and to a photodetecting method using the photodetector.
2. Description of the Related Art
As a photodetector of high sensitivity with a high S/N ratio, an image pickup tube of a high-gain avalanche rushing amorphous photoconductor (Super-HARP) is currently being developed, which uses an amorphous selenium photoconductor as an image pickup tube photoconductive target (“Ultrahigh Sensitivity Super-HARP Image Pickup Tube”; pp. 1189-1198, Journal of Institute of Television Engineers of Japan, Vol. 46, No. 9). This Super-HARP image pickup tube can greatly increase a quantity of electric charges that can be taken out, by using the amorphous selenium photoconductor as a target and by applying a high voltage to the amorphous selenium photoconductor to cause avalanche amplification. In addition, compared with a conventional image pickup tube, an image much higher in quality can be obtained.
However, since the Super-HARP image pickup tube has a vacuum-tube structure and needs electron beam scanning, the photodetector is increased in size, and a size of a photodetection unit is currently limited to about 1 inch.
Thus, a photodetector which is thin but high in both sensitivity and S/N ratio is desired.